It is desirable to provide an improved economical means of motorizing any normal bicycle with a minimum of modification while at the same time employing the compact internal combustion engines which are available in the market. Additionally, it is also desirable to provide auxiliary motor power to normal bicycles having one or more speed gears such as the well known ten speed gear bicycle without modification of the speed gears while retaining the advantage of the speed gear changes whether operating in the engine power mode or pedal power mode.